It has long been customary in the reaction injection molding of fiber reinforced articles to place a preformed batt or mat of the fibrous material, as for example glassfibers, in a mold and then to fill the mold with a hardenable fluid, such as a resin or a mixture of reactive chemicals, at high pressure to impregnate the fibrous mat. The fiber reinforced molded article is removed from the mold when the fluid molding chemical hardens.
The reaction injection mold apparatus of the type with which the present invention is concerned has commonly comprised a two part mold having male and female die parts. The female die part frequently has provided a horizontal partition surface extending around and defining the periphery of an upwardly opening diecavity. In that situation, the male die part has provided a horizontal peripheral partition surface essentially coextensive with the partition surface of the female die part and adapted to seat thereat in sealing relationship to effect a horizontal parting surface for the high pressure mold. The male die part has also provided a male plunger that extended below the male partition surface and projected into the die cavity to form a mold cavity configured to the shape of the article to be molded when the male and female partition surfaces were flush with each other in sealing relationship during the molding operation.
In order to provide fiber reinforced molded articles of uniform quality in production, it is important to assure that the fibrous mat completely fills the mold cavity essentially uniformly and without overlapping or extending between the partition surfaces of the male and female die parts. Otherwise such overlapping portions of the mat prevent an effective seal at the parting surface. On the other hand, if the mat does not completely fill the mold cavity, the molded article will be formed with a "resin enriched" edge or surface portion that will not be adequately reinforced by the fibrous material.
Accordingly, in the reaction injection molding of fiber reinforced articles, it has been conventional to cut one or more mats or batts of the fibrous material to a predetermined size and then stack several of the batts in layers on a preforming frame, according to the weight of reinforcing fiber required or the dimensions of the article to be molded. The fibers of the reinforcing material are usually coated with a thermoplastic binder to facilitate handling. If the binder renders the fibers comparatively stiff at room temperature, the preforming frame is placed in an oven to heat and soften the binder. Thereafter, while the layered batts are warm and readily pliable, they are transferred on the frame to a preforming die press and pressed to a desired predetermined shape to fit closely within the mold of the RIM apparatus. After the layered preformed batt cools, it is removed from the preforming frame and die press, then placed in a trimming press and trimmed to the exact desired final size required for placement in the mold of the RIM apparatus. Thus, the preformed batt will fill the RIM mold cavity uniformly without overlapping the parting surface.
The complex procedure outlined above enables the reaction injection molding of fiber reinforced articles of suitable uniformity and quality when carefully performed, but the multi-step preforming procedure is laborious, costly, and time-consuming.